1. Field of the Invention
The present invention relates to copolymer dispersants useful for dispersing for aqueous media of mineral fillers and/or mineral pigments which-increase the water resistance of dried or drying films made from filled and/or pigmented aqueous compositions, and the filled and/or pigmented aqueous compositions containing the dispersant.
2. Discussion of the Background
Until now, the water-soluble dispersants used for deflocculation in formulations based on pigments or fillers have been subdivided into two different families:
The first family consists of low-molecular-weight acrylic dispersants obtained by radical polymerization in solution, whose principal advantages are a high dispersing effectiveness, exhibited in the ability to prepare a paste using moderate mechanical energy, in which the paste consists of large quantities of mineral pigments and/or mineral fillers in a small volume of water containing the dispersant, and providing good stability of the viscosity of the formulation obtained, both over time and with respect to temperature. These dispersants have a major drawback in their strong hydrophilicity, leading to formulations having a great sensitivity to water during and after drying. This phenomenon is demonstrated particularly in paint formulations by the tests of resistance to wet abrasion conducted on dry films (DIN 53778) and the test of atomization of water on a freshly applied film. PA1 The second family consists of vinyl based dispersants obtained by radical polymerization among which the best known compounds are the diisobutylene-maleic anhydride copolymers, which during drying and after drying impart improved water resistance to the formulations. This is seen notably in paints by the tests of resistance to wet abrasion on a dry film (DIN 53778) and the test of atomization of water on a freshly applied film. These dispersants also have major drawbacks however in exhibiting mediocre dispersing effectiveness and poor rheological stability of the resulting formulations both over time and with respect to temperature. PA1 A represents units resulting from acrylic or methacrylic acid, PA1 B represents units resulting from styrene or a derivative thereof such as .alpha.-methylstyrene or vinyltoluene, PA1 C represents units resulting from C.sub.1 -C.sub.4 alkyl acrylates or methacrylates, PA1 a represents the percentage by weight of the monomer A, with respect to the total weight of the monomers, and a is a value from 40 to 60, PA1 b represents the percentage by weight of the monomer B, with respect to the total weight of the monomers, and b is a value from 25 to 45, PA1 c represents the percentage by weight of the monomer C, with respect to the total weight of the monomers and c is a value from 0 to 20, PA1 wherein the copolymer imparts increased water resistance to filled and/or pigmented compositions while at the same time maintaining a very good dispersing effects. PA1 A represents units resulting from acrylic or methacrylic acid, PA1 B represents units resulting from styrene or a derivative thereof such as .alpha.-methylstyrene or vinyltoluene, PA1 C represents units resulting from C.sub.1 -C.sub.4 alkyl acrylates or methacrylates, PA1 a represents the percentage by weight of the monomer A with respect to the total weight of the monomers, and a is a value from 40 to 60, PA1 b represents the percentage by weight of the monomer B, with respect to the total weight of the monomers, and b is a value from 25 to 45, PA1 c represents the percentage by weight of the monomer C with respect to the total weight of the monomers, and c is a value from 0 to 20,
Until now a person skilled in the art has always confronted the problem of having available only compositions which are not completely satisfactory. Thus the filled and/or pigmented aqueous compositions previously available which are stable over time and with respect to different temperature, form films which when applied as a coating have a great sensitivity to water during and after drying. This leads to various consequences, including either poor washability with regard to interior coatings or poor resistance to weathering, especially to rainfall, which develops early after their application as exterior coatings. This can be observed, for example, by the washing off of thin films, such as mat exterior films. Moreover a person skilled in the art today also has filled and/or pigmented aqueous compositions whose films when applied as a coating are relatively insensitive to water but whose rheologies are unstable over time and with respect to temperature This is seen essentially in an increase of the Brookfield viscosities. This has the drawback that it changes the characteristics of film application such as loading of the roller or the brush. The levelling of the paint results in difficulties of application to the support great difficulty in mixing these paints homogeneously with the pigmented pastes required to achieve the final hue or in impossibility of removing the paint from its packaging due to the fact that it has gelled.